Counterbalance mechanisms have been used for vertically sliding window sashes for a substantial period of time. Weights connected over a pulley to the window sash by ropes, cords, ribbons, bands, chains, and the like (“connectors”) provide sufficient upward force on the sash that the weight thereof is counterbalanced and the sash can easily be lifted and maintained in a stationary position.
Problems exist with such counterbalancing mechanisms. For example, the connector may break, thereby rendering the counterbalance mechanism ineffective. If the connector breaks when the sash is in the closed position and the weight is sufficiently heavy, the weight can fall through the weight pocket, break through the bottom of the window frame and pass into the wall. Fixing such systems may be difficult since counterbalances having a desired weight which are capable of fitting through the opening of the weight pocket may not be readily available.
If the window glass is broken, a lighter or heavier glass may be used to replace the broken glass which, in turn, will cause the original counterbalance weight to improperly counterbalance the new weight of the sash. The force generated by prior art counterbalance devices cannot readily be adjusted for a particular sash in a weight and pulley vertically operating window counterbalance system.
Replacement of broken ropes or chains may also be difficult, since heavy counterbalance weights may have to be assembled when repair is attempted. Further, with heavy sashes, counterbalance weights sometimes require a diameter that is too large to fit into the opening of the window frame to provide sufficient counterbalance weight. If the necessary counterbalance weight is achieved by using a weight having a smaller diameter, it will necessarily be longer to be of an adequate and effective weight to counterbalance a heavy sash. Such longer weights significantly reduce the amount of travel of the sash because the longer weight will more readily contact the bottom of the window frame.